Changes in high energy phosphate (HEP) metabolism has been implicated as a causative factor in the pathophysiologic conditions of post-ischemic mechanical dysfunction ("stunned myocardium") and post-infarction heart failure. To examine this possible relationship, we are applying the emerging methodology of NMR spectroscopy in an isolated heart model to the study of myocardial bioenergetics in these conditions. 31p and 1H NMR spectroscopy offers the unique advantage of noninasive, real-time assessment of dynamic changes in intracellular metabolites and HEP fluxes in intact organ systems. While the understanding of cardiac energy metabolism during normal and pathologic conditions has been greatly advanced using traditional techniques, NMR spectroscopy offers the potential for more detailed understanding of the dynamics of cellular bioenergetics in these pathophysiologic conditions.